With the increased packing density of LSI for example, the circuit scale has remarkably been reduced. With regard to a semiconductor device, the line width thereof has been reduced to less than 0.1 μm. Accordingly, there is a growing demand through the years for the accuracy of an exposure apparatus employed for fabricating such a circuit or device. Thus, low-thermal-expansion-coefficient members have been developed for use in the exposure apparatus.
For example, Japanese Patent Laying-Open No. 11-209171 discloses a dense and low-thermal-expansion ceramic and a member of a semiconductor manufacturing apparatus that is formed of the dense and low-thermal-expansion ceramic. The dense and low-thermal-expansion ceramic contains at least 80% by weight of cordierite and a rare-earth element equivalent to 1–20% by weight of oxide, the ceramic having a porosity of 0.1% or less and a thermal expansion coefficient of 1×10−6/° C. or less at 10–40° C.
Japanese Patent Laying-Open No. 11-343168 discloses a low-thermal-expansion black ceramic further having a light-shielding property that contains at least 80% by weight of cordierite and preferably contains a rare-earth element equivalent to 1–20% by weight of oxide, the ceramic having a porosity of 0.5% or less, a carbon content of 0.1–2.0% by weight, and a thermal expansion coefficient of 1×10−6/° C. or less at 10–40° C. There is also disclosed a member of a semiconductor manufacturing apparatus that is formed of such a dense and low-thermal-expansion ceramic.
The remarkably reduced scale of the circuit requires the exposure accuracy to be maintained for its semiconductor or liquid-crystal glass substrate. Then, for example, a material for a vacuum chuck or stage-position metering mirror of an exposure apparatus must have a low coefficient of thermal expansion as well as high rigidity (Young's modulus). Quartz, aluminum titanate and crystallized glass are examples of conventional low-thermal-expansion materials that have a problem in terms of rigidity.
On the other hand, conventional dense cordierite materials or low-thermal-expansion ceramics disclosed in Japanese Patent Laying-Open Nos. 11-209171 and 11-343168 have a low coefficient of thermal expansion as well as high rigidity.
However, most of such low-thermal-expansion ceramics including the dense cordierite materials have a relatively low wear resistance. When such a conventional low-thermal-expansion ceramic is used in a wafer-holding vacuum chuck of an exposure apparatus, for example, the wafer-holding surface of the chuck that contacts the wafer wears and loses its flatness, and consequently an exposure failure is likely to occur. If the conventional low-thermal-expansion ceramic is used in a stage-position metering mirror, movement of the stage causes wear which highly possibly results in an exposure failure.
In addition, most of the conventional low-thermal-expansion ceramics have electrical insulation property. Accordingly, if such a ceramic is used in the wafer-holding vacuum chuck of an exposure apparatus, static electricity generated, when a wafer is placed on the chuck, cannot be removed and consequently particles are attached to the wafer, resulting in an exposure failure. This problem regarding particles becomes serious as the circuit scale is increasingly reduced. Therefore, a low-resistance ceramic material is desirably used in the vacuum chuck in order to remove the static electricity.
Moreover, in terms of visibility and soil resistance, a ceramic member used for a semiconductor manufacturing apparatus is desirably colored with black for example.